abstract class Express{ public int weight; public abstract int getWeight(); public abstract int getTotal(); } public class SLExpress extends Express{ public int cost; public SLExpress(){ } public SLExpress(int weight){ super.weight=weight; } public int getTotal(int weight){ cost=12+(weight-1)*2; return cost; } } public class DDExpress extends Express{ public int cost; public DDExpress(){ } public DDExpress(int weight){ super.weight=weight; } public int getTotal(int weight){ cost=5+weight-1; return cost; } } public class CaicaiStation{ public int sum; public int calculate(Express[] ex){ for(int i=0;i<ex.length;i++){ sum+=ex[i]; } } }纠错

在这段代码中，`CaicaiStation`类中的`calculate()`方法中有一个错误：

1. 在`sum+=ex[i];`语句中，`ex[i]`是`Express`类型的对象，不能直接进行加法操作，需要调用`ex[i].getTotal()`方法来获取该快递的总费用。

下面是修改后的代码：

abstract class Express {
    public int weight;
    public abstract int getWeight();
    public abstract int getTotal();
}

public class SLExpress extends Express {
    public int cost;

    public SLExpress() {
    }

    public SLExpress(int weight) {
        super.weight = weight;
    }

    public int getWeight() {
        return weight;
    }

    public int getTotal() {
        cost = 12 + (weight - 1) * 2;
        return cost;
    }
}

public class DDExpress extends Express {
    public int cost;

    public DDExpress() {
    }

    public DDExpress(int weight) {
        super.weight = weight;
    }

    public int getWeight() {
        return weight;
    }

    public int getTotal() {
        cost = 5 + weight - 1;
        return cost;
    }
}

public class CaicaiStation {
    public int sum;

    public int calculate(Express[] ex) {
        for (int i = 0; i < ex.length; i++) {
            sum += ex[i].getTotal();
        }
        return sum;
    }
}